PREDICTING OVERHEATING RISK IN HOMES Susie Diamond Inkling Anastasia Mylona CIBSE Simulation for Health and Wellbeing 27th June 2016 - CIBSE
About Inkling Building Physics Consultancy Susie Diamond Claire Das Bhaumik Services Design stage overheating risk assessments Part L2A/CO2 emissions calculations Massing and orientation advice Daylight, sunlight and overshadowing reports EPC predictions Thermal performance and TM54 analyses CFD modelling
Domestic overheating Article by Liza Young CIBSE Journal August 2014 Article by Liza Young CIBSE Journal May 2016
Assessing Overheating risk Zero Carbon Hub publication Co-authored by Inkling and Anastasia Mylona (ARCC and CIBSE) Part of report series and ongoing research
What is overheating? No one definition fits all Comfort is subjective Depends on both environmental and human factors Duration/ timing of high temperatures is important Very high temperatures > 35 C lead to Heat stress High bedrooms temperatures (>26 C) can impair sleep Image from ZCH Overheating in homes - Where to Start - An introduction for planners, designers and property owners, 2013
Key overheating risk factors in homes Single aspect Large areas of glazing Limited ventilation Restricted openings City centre locations Noise and/or air pollution limiting natural ventilation UHI effects Community heating
Higher overheating risk in city centres Image from ZCH publication: Overheating in homes - Where to Start - An introduction for planners, designers and property owners, 2013
Existing Methodologies SAP (Appendix P) Single calculation for June, July and August using monthly averages for weather data Single zone model Easy to fudge CIBSE Guide A 2015 Follows TM52 adaptive thermal comfort Based on commercial buildings - advice for dwellings is limited PHPP Passive House Planning Package Spreadsheet based Uses bespoke internal gains but similar calc to SAP Dynamic Thermal Simulation Powerful software, but inconsistent application as no defined methodology
Evidence?
What do we need? A stakeholder agreed methodology to follow that is: Reliable Cost-effective Flexible Understandable Not as easy as it first appears, but do-able
CIBSE TM52 Developed for free-running commercial buildings Provides a definition of overheating and pass/fail criteria Based on BS EN Standard 15251:2007 Sets three criteria against which designs should be assessed: Criterion 1: Hours of Exceedance Criterion 2: Daily Weighted Exceedance Criterion 3: Upper Limit Temperature
TM52 How it works 1. The first criterion sets a limit for the number of hours that the operative temperature can exceed the threshold comfort temperature (upper limit of the range of comfort temperature) by 1 K or more during the occupied hours of a typical non-heating season (1 May to 30 September). 3% 2. The second criterion deals with the severity of overheating within any one day, which can be as important as its frequency, the level of which is a function of both temperature rise and its duration. This criterion sets a daily limit for acceptability. Weighted exceedance 6 3. The third criterion sets an absolute maximum daily temperature for a room, beyond which the level of overheating is unacceptable. It requires the internal operative temperature not to exceed the external running mean by more than 4 degrees. ΔT 4K
TM52 variable threshold DTM results Threshold temperature graph
TM52 results presentation DTM results zones results for each criteria
Adapting TM52 for homes Occupancy profiles are required (not easy) Domestic occupancy very variable To test design need worst case scenario, but too worst case is excessive and might force mechanical cooling Focusing on occupied hours for bedrooms can have unintended consequences More robust to include all hours i.e. 24/7 TM52 thresholds are these suitable for homes where occupancy hours are longer? Do we need to adapt them?
Domestic profiles Inkling working with Arup and CIBSE to compile profiles based on suggestions from range of sources Lighting and equipment gains linked back to annual electrical consumption for homes This image shows the collated profile for living room occupancy gains. There is significant correlation, but also variation..
Limitations Cannot guarantee that people will always be comfortable, regardless of how they act Will need to consider different sizes of unit Exceptions - should DTM be required on low risk units?
Guidance needed Advice will be required to cover: Recommended sample size Choice of sample - aim for worst case or a varied selection? Weather file selection including when/how to use future weather Use of blinds Modelling window openings
Start somewhere
CIBSE Weather datasets Dynamic thermal simulation building models require external climate inputs. Annual observed weather data at hourly intervals supplied from the Met Office. Weather variables include air temperature, solar radiation and wind. Formats available EPW, TAS,.csv
TRYs and DSYs Test Reference Years (TRYs) The TRY weather file represents a typical year and is used to determine average energy use within buildings. It consists of average months selected from an historical baseline. Previous release in 2006 used a baseline from 1984 to 2004. Design Summer Years (DSYs) The DSY represents a warmer than typical year and is used to evaluate overheating risk within buildings. The previous methodology for selecting the DSY released in 2006 involved calculating the mean temperature over the period April to September for each year in an observational dataset. The DSY was then chosen as the third hottest year. Previous release in 2006 used a baseline from 1984 to 2004.
New TRYs and DSYs Baseline dataset is being updated, both TRY and DSY are selected from 1984 2013 baselines. TRY same methodology, but with updated baseline, any effects of observed changes in climate are now included. DSY methodology for selecting candidate years has changed, based on that used in TM49: New files are selected using new metrics based on interrelations between external temperatures and internal comfort temperatures. Better description of overheating events, their relative severity and their expected frequency.
New TRYs and DSYs Available for 14 locations. For each of 14 locations there are: Current TRY Current DSY1 featuring moderately warm summer Current DSY2 featuring short intense warm spell Current DSY3 featuring long, less intense warm spell Note: three new DSYs to replace the single old one per location.
London DSYs The set also includes the TM49 data made available for London last year with three different London locations: London Gatwick (rural) LGW London Heathrow (sub-urban) LHR London Weather station (inner urban) LWC Including these three sites allows for different degrees of urban heat island (UHI) effect to be included within the data. This effect is known to increase night-time temperatures significantly in built up areas. The advice is to use the data most appropriate to the project site.
New Future TRYs and DSYs The future weather files have been morphed based on the UKCIP09 projections and include the following options for each location: > Future TRY v Future DSY > DSY1 > DSY2 v DSY3 > 2020s (only for high) > 2050s (only for medium and high) v 2080s > Low emissions scenario > Medium emissions scenario v High emissions scenario 10th percentile 50th percentile 90th percentile
Probabilistic Climate Profiles The Probabilistic Climate Profiles (or ProCliPs) were developed by CIBSE to assist the selection of future files appropriate for each project. These charts, available for all 14 locations, are available for free on the CIBSE Knowledge Portal. Seasonal mean air temperature (Winter, Spring, Summer Autumn) Daily minimum temperatures for winter Daily maximum temperatures for summer Seasonal daily precipitation (Winter, Spring, Summer Autumn)
The End Thank you for listening! Find us at www.inklingllp.com : @InklingLLP